I know. I drew holly instead because mistletoe looks too visually indistinct to really work in a comic. There was actually a post about this on webcomics.com a while back. Here’s the gist of it:

DRAWING HOLLY INSTEAD
Readers who don’t recognize mistletoe will understand the visual, and thereby get the joke.
Readers who do recognize mistletoe will get the joke (but might complain that the plant was drawn wrong)

DRAWING MISTLETOE
Readers who don’t recognize mistletoe will not get the joke
Readers who do recognize mistletoe will get the joke.